The invention relates to a reciprocating piston internal combustion engine.
With respect to the technical background, reference is made, for example, to the globally known Harley-Davidson V-twin internal combustion engines with their typical “two-cylinder sound” for Harley-Davidson motorcycles.
A further development of the globally famous V-twin reciprocating piston internal combustion engines took place by way of Jim Feuling's so-called “W3 project”. In this project, in which, as in a V-twin internal combustion engine, the two cylinders are arranged behind one another in a V-shaped manner and the connecting rods act on a common crankpin journal of the crankshaft, Feuling's design has three cylinders, however, which evoke a “W”; hence the “W3” designation. Feuling constructed a novel crankcase, onto which a third cylinder including cylinder head is mounted into the V offset by 45°. The three cylinders together define a single plane. This was made possible by the use of a main connecting rod and two auxiliary connecting rods which share a common crankpin journal of the crankshaft. This is a design which is also still used today in aircraft reciprocating piston internal combustion engines with a radial cylinder arrangement (radial engines). Feuling's globally famous exceptional design is protected firstly by U.S. design Pat. D449,620 S and secondly by U.S. design Pat. Des. 417,674.
A disadvantage of Feuling's W3 design is the large cylinder angle which requires a relatively large amount of installation space.
Another way of implementing a three-cylinder reciprocating piston internal combustion engine is described by German laid open specification DE 10 2008 020 423 A1. This laid open specification discloses a reciprocating piston internal combustion engine with three cylinders in a V-arrangement, in particular for use in a motorcycle. The reciprocating piston internal combustion engine includes a crankshaft and a first outer cylinder, a second outer cylinder and a middle cylinder. Each cylinder is assigned a piston and a connecting rod. The outer cylinders lie in a common plane which passes through the crankshaft axis, and the middle cylinder lies in a second plane which is inclined with respect to said plane and likewise passes through the crankshaft axis. The three-cylinder reciprocating piston internal combustion engine is distinguished by the fact that the crankshaft has two crankpin journals and the connecting rods of the first outer cylinder and of the middle cylinder act jointly on the first crankpin journal and the connecting rod of the second outer cylinder acts on the second crankpin journal.
A disadvantage of the three-cylinder reciprocating piston internal combustion engine which is known from DE 10 2008 020 423 A1 is the relatively large overall width, which has a disadvantageous effect, in particular, when used for a motorcycle.
A further possibility for realizing a three-cylinder reciprocating piston internal combustion engine was shown as early as 1909 by Anzani with his fan-type reciprocating piston internal combustion engine for aircraft. Using this fan-type reciprocating piston internal combustion engine, the Frenchman Blériot in his Blériot IX was the first to fly across the English Channel from France to England as early as 1909. The reciprocating piston internal combustion engine had 25 hp which was impressive at the time and a rotational speed of almost 1200 rpm. The aircraft made a substantial contribution to the development of the later commonplace aircraft design, the monoplane, in which the engine, the wings and, at the rear, a tailplane followed one another in the flying direction from front to back. A foot-operated rudder and an additional control stick for operating the elevator already then corresponded to the currently customary controls of aircraft. Approximately 800 aircraft of this type made it the most widely produced aircraft prior to 1914. In Anzani's design, all three cylinders lay in one plane, in a similar manner to Feuling's design, the outer cylinders defining an angle >90°.
A disadvantage of this design is once again the relatively large cylinder angle which requires a large amount of installation space.
A further possibility for realizing a fan-type machine is described in the Internet lexicon “Wikipedia”, the free encyclopedia. It is stated there that the fan-type machine is a piston machine, in which the power units (power unit: piston, connecting rod, crankshaft throw) are distributed uniformly over half the circumference, in an analogous manner to the radial machine, where they are distributed over the entire circumference. Up to five-cylinder small compressors are customary, in which the connecting rods are arranged next to one another on a single crankshaft journal. Machines are talked about here instead of engines, since in this arrangement there can be (combustion) engines, compressors, pumps and steam machines. However, the pistons or cylinders, as in Feuling's design, also define a single plane in these embodiments.
A disadvantage of this known embodiment is the relatively wide overall design which is not suitable, in particular, for single track vehicles such as motorcycles.
It is an object of the present invention to provide a W3 reciprocating piston internal combustion engine, the cylinder angles of which can be dimensioned largely freely, in order to obtain an overall design which is as compact as possible.
This and other objects are achieved by a reciprocating piston internal combustion engine, having at least a first, a second and a third cylinder and having a crank mechanism with a crankshaft which is mounted rotatably in a crankcase. A first, a second and a third crankpin journal are provided. The first crankpin journal is assigned a first connecting rod with a first piston for the first cylinder. The second crankpin journal is assigned a second connecting rod with a second piston for the second cylinder. The third crankpin journal is assigned a third connecting rod with a third piston for the third cylinder. The crankpin journals are arranged behind one another in an axial orientation of the crankshaft, wherein the cylinders are arranged in a fan-shaped manner.
A type of W3 reciprocating piston internal combustion engine which is not yet known and the cylinder angles of which can be dimensioned largely freely is realized by way of the configuration according to the invention of the reciprocating piston internal combustion engine. “Fan-shaped” is understood to mean that each cylinder lies in a plane which is parallel to the further planes which are formed by the other cylinders. In comparison with other radial engines, the invention therefore makes a narrower cylinder angle possible in the case of the existing cylinder offset. The minimum cylinder angle is dependent on the cylinder offset, the spacing of the crankpin journals on the crankshaft. Moreover, on account of the possible cylinder angles, the invention makes it possible to implant a W3 engine virtually in the installation space of a V-twin engine; the overall width increases in a non-critical range. Accordingly, for a four-cylinder internal combustion engine, the cylinder angle of a W4 is only insubstantially greater than in the case of a V4. The sound of a V-twin internal combustion engine can likewise be replicated by way of an internal combustion engine of this type according to the invention; the sound can even be designed to be somewhat “fresher”.
Particularly satisfactory rigidity of the crankshaft is achieved by providing, in each case, one bearing point between the crankpin journals.
A cylinder angle α of 20° to 90° between adjacent cylinders is a particularly preferred design range.
The at least two cylinder angles α have unequal angular dimensions in a further development of the invention. Even more design options are made possible as a result.
An embodiment wherein a mass balancing shaft, which can be driven by the crankshaft and is oriented parallel to the crankshaft, advantageously influences the running properties or the smooth running (NVH=noise, vibration, harshness) of the reciprocating piston internal combustion engine according to the invention.
The reciprocating piston internal combustion engine according to the invention is particularly preferably used for a single track vehicle, and can preferably be installed transversely with respect to a driving direction of the single track vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.